Two-Bond 19F−15N Spin−Spin Coupling Constants (2hJF-N) across F−H···N Hydrogen Bonds
Equation-of-motion coupled cluster calculations (EOM-CCSD) have been performed to determine two-bond 19F−15N spin−spin coupling constants (2hJF-N) for thirteen neutral complexes stabilized by F−H···N hydrogen bonds. The proton acceptors include nitrogens that are sp (HCN and its derivatives), sp2 (aromatic azines), and sp3 (NH3 and its derivatives) hybridized. 2hJF-N is determined by the Fermi-contact term, which is strongly dependent on the intermolecular F−N distance but varies only slightly with small perturbations of the hydrogen bond from linearity. 2hJF-N is more sensitive to the hybridization and bonding at the nitrogen in F−H···N hydrogen bonds than is 2hJN-N for complexes stabilized by N−H−N and N−H+−N hydrogen bonds. As a result, 2hJF-N at the same F−N distance for different complexes can vary by 10−15 Hz, and this reduces the quality of the quadratic curve used to relate 2hJF-N to the F−N distance. However, if the complexes are grouped according to the hybridization of the nitrogen, excellent quadratic correlations are found between 2hJF-N and the F−N distance. Moreover, if the same groupings are used, 2hJF-N also correlates with the charge density at the bond critical point of the hydrogen bond.